The study will produce a genetic map of the genus Prunus, which includes cherry, peach, plum, apricot and almond. Horticulture Research International, based at East Malling in Kent - which has a 60-year history of research into cherry varieties - will co-operate with scientists in Spain, who will work on the almond, and Italy and France, who will work on the peach. Ken Torbutt, the project leader at HRI, says the genetic map will allow breeders to choose the fruit, nut or timber qualities they want in seedlings rather than waiting years for trees to mature before the results of crosses become apparent.
In effect, this is the tree equivalent of the Human Genome Project - an international collaboration to find the position of every gene on the 23 pairs of human chromosomes. But it is on a much smaller scale. Prunus has eight chromosomes, and the study will be looking for the genes controlling 250 characteristics. The project involves establishing the position of a set of genes called markers, which are 'signposts' to the position of the genes that control the characteristics of interest to breeders.
These marker genes can then be identified from small tissue samples taken from seedlings, using a technique called the polymerase chain reaction. This technique allows multiple copies of a particular gene to be produced, making it easy to identify.' Our aim is to show how cherry genes are arranged on the chromosomes. By identifying the genes responsible for flavour, flesh colour, fruit size, vigour, pest and disease resistance, and branch angle - and establishing the position of marker genes - we can enable breeders to predict the presence of desirable characteristics even in a tiny seedling,' says Mr Torbutt.
'This means new seedlings can be selected up to 10 times faster than at present.'
There are 300 varieties of sweet cherries in the national collection, of which 10 - such as Stella and Van Merchant - are commercially dominant.
HRI is not just interested in sweet cherries. It breeds for rootstock and is also researching new varieties of Prunus avium that would be suitable as timber trees. Cherry produces a high-value reddish wood that It grows faster than oak and is resistant to damage by the grey squirrel. One important characteristic is branch angle - a timber trees should have an upright habit, because this limits the possibility of getting disease in the angle, which causes ugly knots in the wood when the branch snaps off.
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